1. Field of the Invention
The present invention relates to a method for cleaning a curing mold to be used for manufacturing elastomer articles, and in particular relates to a cleaning method by eliminating curing residual of elastomer stuck to the mold without damaging the mold.
In this specification, the term "elastomer" means rubber or rubbery elastic compound before curing by the mold, and the phrase "curing residual" means contamination of elastomer and compounded carbon black, zinc white and so on which is stuck to for example the cavity surface of the mold in the course of use in repeated curing processes.
2. Description of the Prior Art
A tire curing mold is a typical curing mold, one example of which is called an inserter mold. As described in Japanese laid-open patent specification 223108/92 (corresponding to EP-0451832), an inserter mold is made of nine or so divided molds each of which is made of many pieces, and consequently one inserter mold is composed of several hundred pieces.
An inserter mold has no air-vent, namely it is a spewless type mold due to the reason that about 80 .mu.m clearances (slits) between the pieces fulfil the function of an air-vent.
In general, the above-mentioned curing residual stuck to such as the surface of the mold cavity, air-vent, inside of slits (clearances) and so on remains as it is, and the amount of the curing residual increases after repetition of the curing process. As curing residual stuck to the mold has an adverse influence on the quality of elastomer articles, it is necessary to remove the same. Usually, the mold is cleaned to remove curing residual at the predetermined frequency of the curing process.
The shot blast method and liquid cleaning method are known as typical methods for cleaning molds.
The shot blast method is a method for cleaning the mold by blowing plastic beads at high pressure onto the mold. The liquid cleaning method is a method for cleaning the mold by utilizing strong acid such as hydrochloric acid, sulfuric acid or nitric acid or strong alkali such as caustic soda or amine liquid of organic alkali.
There are some difficulties in the above-mentioned prior art mold cleaning methods. In the case of the shot blast method, as for curing residual stuck to the cavity surface of the mold, it is possible to clean the same by means of striking directly by blowing plastic beads at high pressure, but as for curing residual stuck to the air-vent and inside of slits (clearances) such as in a tire curing mold, plastic beads cannot reach there directly and it is impossible to eliminate the same. Moreover, the air-vent is sometimes blocked by crushed plastic beads, to prevent the passage of air. Further, as the mold is usually made of material mainly composed of aluminium, it does not have enough strength to avoid physical damage such as wear or transformation of edge portions due to impact of plastic beads, letters and marks on the mold easily become unclear, and also sharpness of pattern configuration is lost.
In particular, as mentioned before, an inserter mold has so many clearances (slits) between the pieces, the clearances are easily blocked by crushed plastic beads and projected rubber is easily stuck thereto and the clearances between mold pieces tend to become narrower due to deformed burrs (flash) at the edge portion. In the case of the shot blast method, it is very difficult to eliminate plastic beads and/or projected rubber blocked between the mold pieces. To clean an inserter mold, it is dismantled into several hundred pieces for cleaning each of them and eliminating deformed burrs (flash) at the edge portions after which all the pieces are assembled into one mold.
On the other hand, in the case of the liquid cleaning method, it is possible to eliminate more easily curing residual stuck to the air-vent and inside of slits (clearances) and there occur neither wear of mold by plastic beads nor blocking by crushed plastic beads. From these points of view, the liquid cleaning method is better than the shot blast method. However, the liquid cleaning method has other defects, namely the metal mold made of base material of aluminium is corroded by acid or alkali liquid, and amine liquid of organic alkali is not only expensive but also regulated to be hazardous materials of third class petroleums, fourth group in Japanese regulations which result in the necessity of various kinds for safety countermeasures.
An object of the present invention is to develop a method for cleaning molds by eliminating curing residual stuck to the mold surface without damaging the mold and without reducing safety and efficiency of cleaning work.